General principles of cathodic protection in seawater
This European Standard covers the general principles of cathodic protection when applied in seawater, brackish waters and marine mud. It is intended to be an introduction, to provide a link between the theoretical aspects and the practical applications, and to constitute a support to the other European Standards devoted to cathodic protection of steel structures in seawater.
This European Standard specifies the criteria required for cathodic protection. It provides recommendations and information on reference electrodes, design considerations and prevention of the secondary effects of cathodic protection.
The practical applications of cathodic protection in seawater are covered by the following standards:
- EN 12495, Cathodic protection for fixed steel offshore structures;
- EN ISO 13174, Cathodic protection of harbour installations (ISO 13174);
- EN 12496, Galvanic anodes for cathodic protection in seawater and saline mud;
- EN 13173, Cathodic protection for steel offshore floating structures;
- EN 16222, Cathodic protection of ship hulls;
- EN 12474, Cathodic protection of submarine pipelines;
- ISO 15589 2, Petroleum, petrochemical and natural gas industries - Cathodic protection of pipeline transportation systems - Part 2: Offshore pipelines.
For cathodic protection of steel reinforced concrete whether exposed to seawater or to the atmosphere, EN ISO 12696 applies.
Allgemeine Grundsätze des kathodischen Korrosionsschutzes in Meerwasser
Diese Europäische Norm legt allgemeine Grundsätze des kathodischen Korrosionsschutzes fest, wenn dieser in Meerwasser, Brackwasser und Meeresschlick angewendet wird. Sie dient als Einleitung, als Verbindung zwischen den theoretischen Aspekten und den praktischen Anwendungen sowie als Unterstützung zu anderen Europäischen Normen, die kathodischen Korrosionsschutz von Anlagen aus Stahl in Meerwasser behandeln.
Diese Europäische Norm legt die Kriterien, die für den kathodischen Korrosionsschutz erforderlich sind, fest. Sie gibt Empfehlungen und Informationen zu Referenzelektroden, Design-Überlegungen und Prävention der Nebenwirkungen des kathodischen Korrosionsschutzes.
Die praktischen Anwendungen des kathodischen Korrosionsschutzes in Meerwasser werden von den folgenden Normen abgedeckt:
EN 12495, Kathodischer Korrosionsschutz von ortsfesten Offshore-Anlagen aus Stahl
EN ISO 13174, Kathodischer Korrosionsschutz für Hafenbauten (ISO 13174)
EN 12496, Galvanische Anoden für den kathodischen Schutz in Seewasser und salzhaltigem Schlamm
EN 13173, Kathodischer Korrosionsschutz für schwimmende Offshore-Anlagen aus Stahl
EN 16222, Kathodischer Korrosionsschutz von Schiffen
EN 12474, Kathodischer Korrosionsschutz für unterseeische Rohrleitungen
ISO 15589-2, Petroleum, petrochemical and natural gas industries - Cathodic protection of pipeline transpor-tation systems - Part 2: Offshore pipelines
Für den kathodischen Korrosionsschutz von Meerwasser oder der Luft ausgesetztem Stahl in Beton gilt EN ISO 12696.
Principes généraux de la protection cathodique en eau de mer
La présente Norme européenne traite des principes généraux de la protection cathodique appliquée en eau de mer, en eaux saumâtres et dans les boues marines. Son rôle est de servir d'introduction et de lien entre les aspects théoriques et les applications pratiques et de constituer une base d'appui aux autres Normes européennes dédiées à la protection cathodique des ouvrages en acier en eau de mer.
La présente Norme européenne spécifie les critères requis pour la protection cathodique. Elle fournit des recommandations et des informations sur les électrodes de référence, les considérations pour la conception et sur la prévention des effets secondaires de la protection cathodique.
Les applications pratiques de la protection cathodique dans l'eau de mer sont couvertes par les normes suivantes :
- EN 12495, Protection cathodique des structures en acier fixes en mer ;
- EN ISO 13174, Protection cathodique des installations portuaires (ISO 13174) ;
- EN 12496, Anodes galvaniques pour la protection cathodique dans l'eau de mer et les boues salines ;
- EN 13173, Protection cathodique des structures en acier flottant en mer ;
- EN 16222, Protection cathodique des coques de bateaux ;
- EN 12474, Protection cathodique des canalisations sous-marines ;
- ISO 15589-2, Industries du pétrole et du gaz naturel — Protection cathodique des systèmes de transport par conduites — Partie 2 : conduites en mer.
Pour la protection cathodique du béton armé, exposé à l'eau de mer ou à l'atmosphère, l'EN ISO 12696 s'applique.
Splošna načela za katodno zaščito v morski vodi
EN 12473 zajema splošna načela za katodno zaščito, ko se uporablja v morski vodi, polslanih vodah in slanem blatu. Namenjen je kot uvod, za določitev povezave med teoretskimi vidiki in praktičnimi vrstami uporabe ter za podporo drugim evropskim standardom, ki obravnavajo katodno zaščito jeklenih konstrukcij v morski vodi. Ta evropski standard določa merila, potrebna za katodno zaščito. Podaja priporočila in informacije o referenčnih elektrodah, projektiranju in preprečevanju sekundarnih učinkov katodne zaščite. Praktično uporabo katodne zaščite v morski vodi zajemajo ti standardi: – EN 12495, Katodna zaščita jeklenih konstrukcij, postavljenih v morju ali ob morju; – EN ISO 13174, Katodna zaščita za pristaniške napeljave (ISO 13174); – EN 12496, Galvanske anode za katodno zaščito v slani vodi in slanem blatu; – EN 13173, Katodna zaščita za plavajoče jeklene priobalne konstrukcije; – EN 16222, Katodna zaščita ladij; – EN 12474, Katodna zaščita podmorskih cevovodov; – ISO 15589-2, Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina – Katodna zaščita cevovodov – 2. del: Cevovodi na morju. Za katodno zaščito armiranega betona, ki je izpostavljen morski vodi ali atmosferi, velja standard EN ISO 12696.
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Allgemeine Grundsätze des kathodischen Korrosionsschutzes in MeerwasserPrincipes généraux de la protection cathodique en eau de merGeneral principles of cathodic protection in seawater47.020.01Splošni standardi v zvezi z ladjedelništvom in konstrukcijami na morjuGeneral standards related to shipbuilding and marine structures25.220.40Kovinske prevlekeMetallic coatingsICS:Ta slovenski standard je istoveten z:EN 12473:2014SIST EN 12473:2014en,fr,de01-julij-2014SIST EN 12473:2014SLOVENSKI
STANDARDSIST EN 12473:20001DGRPHãþD
SIST EN 12473:2014
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
February 2014 ICS 47.020.01; 77.060 Supersedes EN 12473:2000English Version
General principles of cathodic protection in seawater
Principes généraux de la protection cathodique en eau de mer
Allgemeine Grundsätze des kathodischen Korrosionsschutzes in Meerwasser This European Standard was approved by CEN on 16 November 2013.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2014 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 12473:2014 ESIST EN 12473:2014
EN 12473:2014 (E) 2 Contents Page Foreword .4 1 Scope .5 2 Normative references .5 3 Terms, definitions, abbreviations and symbols .5 4 Application of cathodic protection in seawater .9 4.1 General .9 4.2 Galvanic anode method .9 4.3 Impressed current method . 10 4.4 Hybrid systems . 10 5 Determination of level of cathodic protection . 12 5.1 Measurement of protection level . 12 5.2 Reference electrodes . 12 5.3 Potentials of reference electrodes . 12 5.4 Verification of reference electrodes. 12 5.5 Potential measurement . 12 6 Cathodic protection potential criteria . 13 6.1 General . 13 6.2 Carbon-manganese and low alloy steels . 13 6.3 Other metallic materials . 15 6.3.1 General . 15 6.3.2 Stainless steels . 15 6.3.3 Nickel alloys . 16 6.3.4 Aluminium alloys . 16 6.3.5 Copper alloys . 17 7 Design considerations . 17 7.1 Introduction . 17 7.2 Technical and operating data . 17 7.2.1 Design life . 17 7.2.2 Materials of construction . 17 7.3 Surfaces to be protected . 18 7.4 Protective coatings . 18 7.5 Availability of electrical power . 18 7.6 Weight limitations . 18 7.7 Adjacent structures . 18 7.8 Installation considerations . 18 7.9 Current demand . 19 8 Effect of environmental factors on current demand . 19 8.1 Introduction . 19 8.2 Dissolved oxygen . 19 8.3 Sea currents . 19 8.4 Calcareous deposits . 19 8.5 Temperature . 20 8.6 Salinity . 20 8.7 pH . 21 8.8 Marine fouling . 21 8.9 Effect of depth . 21 8.10 Seasonal variations and storms . 21 SIST EN 12473:2014
EN 12473:2014 (E) 3 9 Secondary effects of cathodic protection . 21 9.1 General . 21 9.2 Alkalinity . 22 9.3 Environmentally-assisted cracking . 22 9.3.1 General . 22 9.3.2 Hydrogen embrittlement . 22 9.3.3 Corrosion fatigue . 22 9.4 Chlorine . 23 9.5 Stray currents and interference effects . 23 10 Use of cathodic protection in association with coatings . 24 10.1 Introduction . 24 10.2 Coating selection . 24 10.3 Coating breakdown . 25 Annex A (informative)
Corrosion of carbon-manganese and low-alloy steels . 26 A.1 Nature of metallic corrosion . 26 A.2 Polarization . 27 Annex B (informative)
Principles of cathodic protection . 30 Annex C (informative)
Reference electrodes . 33 C.1 General . 33 C.2 Silver/silver chloride/seawater electrode . 33 C.3 The zinc/seawater electrode . 35 C.4 Verification of reference electrodes . 35 Annex D (informative)
Corrosion of metallic materials other than carbon-manganese and low-alloy steels typically subject to cathodic protection in seawater . 37 D.1 Stainless steels . 37 D.2 Nickel alloys . 37 D.3 Aluminium alloys . 37 D.4 Copper alloys . 38 Bibliography . 39
SIST EN 12473:2014
EN 12473:2014 (E) 4 Foreword This document (EN 12473:2014) has been prepared by Technical Committee CEN/TC 219 “Cathodic protection”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 2014, and conflicting national standards shall be withdrawn at the latest by August 2014. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document supersedes EN 12473:2000. According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 12473:2014
EN 12473:2014 (E) 5 1 Scope This European Standard covers the general principles of cathodic protection when applied in seawater, brackish waters and marine mud. It is intended to be an introduction, to provide a link between the theoretical aspects and the practical applications, and to constitute a support to the other European Standards devoted to cathodic protection of steel structures in seawater. This European Standard specifies the criteria required for cathodic protection. It provides recommendations and information on reference electrodes, design considerations and prevention of the secondary effects of cathodic protection. The practical applications of cathodic protection in seawater are covered by the following standards: — EN 12495, Cathodic protection for fixed steel offshore structures; — EN ISO 13174, Cathodic protection of harbour installations
(ISO 13174); — EN 12496, Galvanic anodes for cathodic protection in seawater and saline mud; — EN 13173, Cathodic protection for steel offshore floating structures; — EN 16222, Cathodic protection of ship hulls; — EN 12474, Cathodic protection of submarine pipelines; — ISO 15589-2, Petroleum, petrochemical and natural gas industries — Cathodic protection of pipeline transportation systems — Part 2: Offshore pipelines. For cathodic protection of steel reinforced concrete whether exposed to seawater or to the atmosphere, EN ISO 12696 applies. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 50162, Protection against corrosion by stray current from direct current systems EN ISO 8044, Corrosion of metals and alloys — Basic terms and definitions (ISO 8044) 3 Terms, definitions, abbreviations and symbols For the purposes of this document, the terms and definitions given in EN ISO 8044 and the following apply. NOTE The definitions given below prevail on their versions in EN ISO 8044. 3.1 acidity presence of an excess of hydrogen ions over hydroxyl ions (pH < 7) 3.2 alkalinity presence of an excess of hydroxyl ions over hydrogen ions (pH > 7) SIST EN 12473:2014
EN 12473:2014 (E) 6 3.3 anaerobic condition absence of free oxygen dissolved in the electrolyte 3.4 calcareous deposits minerals precipitated on the metallic cathode because of the increased alkalinity caused by cathodic protection 3.5 cathodic disbondment failure of adhesion between a coating and a metallic surface that is directly attributable to the application of cathodic protection 3.6 cathodic protection system entire installation that provides cathodic protection Note 1 to entry: It may include anodes, power source, cables, test facilities, isolation joints, electrical bonds. 3.7 coating breakdown factor fc ratio of cathodic current density for a coated metallic material to the cathodic current density of the bare material 3.8 copper/copper sulphate reference electrode reference electrode consisting of copper in a saturated solution of copper sulphate 3.9 dielectric shield alkali resistant organic coating applied to the structure being protected in the immediate vicinity of an impressed current anode to enhance the spread of cathodic protection and minimize the risk of hydrogen damage to the protected structure in the vicinity of the anode 3.10 driving voltage difference between the structure/electrolyte potential and the anode/electrolyte potential when the cathodic protection is operating 3.11 electro-osmosis passage of a liquid through a porous medium under the influence of a potential difference 3.12 environmentally assisted cracking cracking of a susceptible metal or alloy due to the conjoint action of an environment and stress 3.13 groundbed system of immersed electrodes connected to the positive terminal of an independent source of direct current and used to direct the cathodic protection current onto the structure being protected 3.14 hydrogen embrittlement process resulting in a decrease of the toughness or ductility of a metal due to absorption of hydrogen SIST EN 12473:2014
EN 12473:2014 (E) 7 3.15 hydrogen stress cracking HSC cracking that results from the presence of hydrogen in a metal and tensile stress (residual and/or applied) Note 1 to entry: HSC describes cracking in metals which may be embrittled by hydrogen produced by cathodic polarization without any detrimental effect caused by specific chemicals such as sulphides. 3.16 isolating joint (or coupling) electrically discontinuous joint or coupling between two lengths of pipe, inserted in order to provide electrical discontinuity between them 3.17 master reference electrode reference electrode, calibrated with the primary calibration reference electrode, used for verification of reference electrodes used for field or laboratory measurements 3.18 over-polarization occurrence in which the structure to electrolyte potentials are more negative than those required for satisfactory cathodic protection Note 1 to entry: Over-polarization provides no useful function and might even cause damage to the structure. 3.19 pitting resistance equivalent PREN indication of the resistance of a corrosion resistant alloy to pitting in the presence of water, chlorides and oxygen or oxidation environment, accounting for the beneficial effects of nitrogen Note 1 to entry: For the purposes of this standard, PREN is calculated as follows: PREN = % Cr + 3,3[(% Mo) + 0,5 (% W)] + 16 (% N). 3.20 potential gradient difference in potential between two separate points in the same electric field 3.21 primary calibration reference electrode reference electrode used for calibration of master reference electrodes is the normal hydrogen electrode (N.H.E.) Note 1 to entry: The official reference electrode, standard hydrogen electrode (S.H.E.), which considers the fugacity coefficient for hydrogen gas and the activity coefficient for H+ ions, is practically impossible to manufacture. 3.22 protection current current made to flow into a metallic structure from its electrolytic environment in order to achieve cathodic protection of the structure 3.23 reference electrode electrode having a stable and reproducible potential that is used as a reference in the measurement of electrode potentials SIST EN 12473:2014
EN 12473:2014 (E) 8 Note 1 to entry: Some reference electrodes use the electrolyte in which the measurement is carried out. Their potential varies according to the composition of this electrolyte. 3.24 resistivity (of an electrolyte) resistivity is the resistance of an electrolyte of unit cross section and unit length Note 1 to entry: of dissolved salts in the electrolyte. 3.25 saturated calomel reference electrode reference electrode consisting of mercury and mercurous chloride in a saturated solution of potassium chloride 3.26 silver/silver chloride reference electrode reference electrode consisting of silver, coated with silver chloride, in an electrolyte containing a known concentration of chloride ions Note 1 to entry: Silver/silver chloride/ saturated KCl electrodes are electrodes currently used in the laboratory and for master reference electrode. Note 2 to entry: Silver/silver chloride/seawater (Ag/AgCl/seawater) electrodes are electrodes currently used for field measurements in seawater. 3.27 slow strain rate test test for evaluating susceptibility of a metal to environmentally assisted cracking (3.12 in this document) that most commonly involves pulling a tensile specimen to failure in a representative environment at a constant displacement rate chosen to generate nominal strain rates usually in the range 10−5 s−1 to 10−8 s−1 Note 1 to entry:
Slow strain rate testing may also be applied to other specimen geometries, e.g. bend specimens. 3.28 specified minimum yield strength SMYS minimum yield strength prescribed by the specification under which steel components are manufactured, obtained through standard analysis and representing a probabilistic value Note 1 to entry: It is an indication of the minimum stress steel components may experience that will cause plastic (permanent) deformation (typically 0,2 %). 3.29 stray currents current flowing through paths other than the intended circuits 3.30 structure to electrolyte potential difference in potential between a structure and a specified reference electrode in contact with the electrolyte at a point sufficiently close to, but without actually touching the structure, to avoid error due to the voltage drop associated with any current flowing in the electrolyte 3.31 sulphate reducing bacteria SRB group of bacteria that are found in most soils and natural waters, but active only in conditions of near neutrality and absence of oxygen and that reduce sulphates in their environment, with the production of sulphides and accelerate the corrosion of structural materials SIST EN 12473:2014
EN 12473:2014 (E) 9 3.32 telluric currents electrical currents induced by time varying changes in the earth's magnetic field Note 1 to entry: They are able to flow in metallic conductors laid in the soil or in the sea. 3.33 zinc reference electrode electrode consisting of pure zinc or zinc alloy specific for anodes in contact with the electrolyte in which the measurements are carried out Note 1 to entry: Zinc reference electrodes are currently used for measurements in seawater carried out at permanent locations. 4 Application of cathodic protection in seawater 4.1 General Metallic materials in aqueous environments such as seawater are susceptible to corrosion produced by electrochemical reactions. General information on corrosion of carbon-manganese or low alloy steels is given in Annex A. Cathodic protection is an electrochemical corrosion prevention system based on the decrease of corrosion potential to a level at which the corrosion rate of the metal is significantly reduced (EN ISO 8044). For industrial structures, residual corrosion rates less than 10 µm / yr are typically achieved with a fully effective cathodic protection system. Cathodic protection is achieved by applying a voltage able to supply sufficient current to the metallic surface to lower the potential. General information on the principles of cathodic protection is given in Annex B. There are two methods whereby the protection current can be supplied to polarize the surface: a) galvanic anode systems in which the current for protection is provided by a metal of more negative corrosion potential than the item to be protected i.e. aluminium, zinc and magnesium alloys for steel and iron for copper and copper based alloys, b) impressed current systems in which direct current (normally produced from alternating current by a transformer rectifier) is used in conjunction with relatively inert anodes such as graphite, thin coatings of platinum or activated mixed metal oxides on metals such as titanium or niobium, lead alloys, silicon-iron, etc; in some cases a consumable anode such as scrap iron or steel is used. 4.2 Galvanic anode method If two dissimilar metals are connected in the same electrolyte, a galvanic cell is produced. The open circuit voltage is the natural potential difference which exists between the two metals. If the circuit is closed, the potential difference drives an electrical current. The more negative electrode behaves as an anode and it releases electrons to the circuit and dissolves more rapidly while the more positive electrode behaves as a cathode and dissolves less readily. The use of galvanic anodes in cathodic protection is based on this phenomenon. Assuming the structure to be protected is made of steel, aluminium or zinc alloy galvanic anodes can be used to form the cell, because these alloys are less noble (more electronegative) than steel. Anode attachment to the structure is made through a steel core on to which the anode material is cast. Thus the structure is in metallic contact with the anode material and also in electrolytic contact with it once the structure is immersed. This is represented in Figure 1, where it is seen that the electrons released by the dissolution of metal atoms are consumed in the cathodic reduction of oxygen on the structure and hydroxyl ions are produced at the structure surface. SIST EN 12473:2014
EN 12473:2014 (E) 10 4.3 Impressed current method Most impressed current anodes are of a type that do not dissolve readily on anodic polarization but sustain alternative reactions which involve decomposition of the aqueous environment, or oxidizing of dissolved chloride ions in it, i.e: 222HOO4H4e−+→++ (1) 22ClCl2e−−→+ (2) Figure 2 represents an impressed current cathodic protection system using an inert anode in seawater where in the secondary reactions hydrogen and chlorine are evolved. The advantages of the impressed current system are that it is possible to have a large adjustable driving voltage so that relatively few anodes need to be installed even to protect large uncoated structures in comparatively high resistivity environments. A comparison of galvanic and impressed current anode systems is given in Table 1. 4.4 Hybrid systems These comprise a combination of galvanic anodes and externally powered impressed current anodes. Because there can be a significant time between the initial immersion of a structure and the full commissioning of the impressed current system it is usual to fit sufficient galvanic anodes to polarize the critical region of the structure. The galvanic anodes should also provide protection when the impressed current system is shut down for subsea survey and maintenance during the life of the structure.
Key 1 seawater 2 galvanic anode 3 anode attachment 4 protected structure in seawater Figure 1 — Representation of cathodic protection using a galvanic anode on a structure in the seawater SIST EN 12473:2014
EN 12473:2014 (E) 11
Key 1 insulated cathode cable 2 power supply (dc) 3 insulated anode cable 4 seawater 5 impressed current anode 6 protected structure in seawater Figure 2 — Representation of impressed current cathodic protection using inert anode in seawater Table 1 — Comparison of galvanic and impressed current systems
Galvanic systems Impressed current systems Environment Use can be impracticable in soils or waters of high resistivity. Use is not restricted by resistivity of soils or waters Installation Simple to install. Needs careful design otherwise can be complicated. Power source Independent of any source of electric power. Cannot be wrongly connected electrically. External supply necessary. Care needs to be taken to avoid electrical connection in wrong direction. Anodes Bulk of anode material can restrict water flow and introduce turbulence and drag penalties. Usually lighter and few in